France will wait for UN inspectors to issue their report on a probe into a chemical weapons attack in Syria before launching any military action against the Damascus regime, French President Francois Hollande said on Friday.

"Are we going to wait for the inspectors' report? Yes, we are going to wait for the inspectors' report as we are going to wait for the US Congress vote" on the proposed strikes, he said after the G20 summit in Saint Petersburg.

Earlier President Barack Obama on Friday said the United States valued France's support for military action against Syrian President Bashar al-Assad's regime for allegedly using chemical weapons against its own people.

"I value very much President Hollande's commitment to a strong international response for these grievous acts," he said, adding that "any action that we contemplate… would be limited and would be focused on deterring the use of chemical weapons in the future and degrade the Assad regime's capacity to use chemical weapons."

Obama was speaking at the G20 summit in St Petersburg, which has been marked by tensions between the various powers over to react to the Syria crisis.

Earlier in the day France said it wants the European Union to unanimously condemn a chemical weapons attack near Damascus and agree it was carried out by the Syrian regime, Foreign Minister Laurent Fabius said Friday before meeting his European counterparts.

He told AFP that at the meeting in Lithuanian capital Vilnius, ministers of the 28-nation bloc should at least secure an agreement that "condemns the usage of chemical weapons and (which) notes that the proof that we have been given shows that it was the regime of Bashar al-Assad which was behind the massacre".

On Thursday night World powers failed to bridge deep divisions on Syria at a summit dinner as they squared off over the US push for military strikes against the Damascus regime.

As tensions over the Syrian conflict threatened to torpedo the working schedule of the G20 summit outside Saint Petersburg, host Vladimir Putin invited participants to air their views over dinner.

The leaders took turns over three hours to reiterate their positions on the issue in 10-minute speeches, a diplomatic source close to the talks told AFP.

"The G20 has just now finished the dinner session at which the divisions about Syria were confirmed," Italian Prime Minister Enrico Letta, who attended the dinner, said on his official Twitter feed.

Russia has led opposition to any US-led military action against Assad's regime over an August 21 chemical weapons attack outside Damascus, which Washington says was perpetrated by Damascus.

In New York, the US envoy to the United Nations accused Russia of holding the UN Security Council hostage.

British Prime Minister David Cameron said London had fresh evidence of chemical weapons use.

The UN announced that its special envoy Lakhdar Brahimi would attend meetings at the two-day summit to push for peace talks.